Multi-stage centrifugal compressor

ABSTRACT

A multi-stage centrifugal compressor, including:a rotary electric motor inside a motor housing and coupled to a motor shaft;two radial compression stages comprising back-to-back bladed compression impellers;an outlet manifold in communication with second exhaust flow paths;at least one inter-stage flow passage comprising:a main channel passing through the motor housing and opening onto a first lateral face of the motor housing;an intermediate channel in sealed communication with the main channel and passing through a spacer inserted between a second lateral face of the motor housing and a second cowl; anda secondary channel formed in the second cowl and opening opposite a second bladed compression impeller.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of PCT Application No. PCT/FR2021/051439 filed on Aug. 3, 2021, which claims priority to French Patent Application No. 20/08282 filed on Aug. 5, 2020, the contents each of which are incorporated herein by reference thereto.

TECHNICAL FIELD

The present disclosure relates to a multi-stage centrifugal compressor, whose function is to compress a gaseous fluid in at least two successive compression stages.

A multi-stage centrifugal compressor is known in particular from document EP1749992, wherein there is an intermediate manifold of the volute type which surrounds the first downstream end of the first bladed compression impeller to recover the compressed gaseous fluid at the outlet of the first stage, and an outlet manifold of the volute type which surrounds the second downstream end of the second bladed compression impeller to recover the compressed gaseous fluid at the outlet of the second stage. Moreover, the inter-stage flow passage of gaseous fluid is formed by an outer pipe which connects the intermediate manifold of the volute type to a second cowl facing the second upstream end of the second bladed compression impeller, in order to provide an axial injection of the gaseous fluid at this second upstream end.

A drawback of the compressor known from document EP1749992 is its size, due to the use of an outer pipe, located outside the motor housing.

Moreover, during the compression of the gaseous fluid at the level of the first stage, the temperature will increase, thus reducing its density and increasing the volume flow rate and therefore the necessary passage sections. In a multi-stage centrifugal compressor, it is therefore preferable to cool the gaseous fluid between two compression stages, to limit the final temperature of the gaseous fluid and thus be able to reduce the size of the components and the energy consumption, and to be able to improve the performance.

Also, in a compressor equivalent to that of document EP1749992, it is possible to use an outer heat exchanger between the outer pipe and a cold source, which again affects the size of the compressor.

The present disclosure proposes to solve all or part of the aforementioned drawbacks, by providing a multi-stage centrifugal compressor having an architecture with improved compactness.

BRIEF SUMMARY

Another object of the present disclosure is to provide a solution for cooling the gaseous fluid between two compression stages, without harming the size and preferably in an economical manner.

To this end, the present disclosure proposes a multi-stage centrifugal compressor, including:

-   -   a rotary electric motor arranged inside a motor housing having         two opposite lateral faces, namely a first lateral face and a         second lateral face;     -   a motor shaft driven in rotation around a motor axis by said         rotary electric motor and having a first section and a second         opposite section extending on either side of the rotary electric         motor and the two respective lateral faces of the motor housing;     -   a first radial compression stage including a first bladed         compression impeller coupled in rotation to the first section of         the motor shaft and having a first upstream end in communication         with a gaseous fluid inlet and a first downstream end facing the         side of the first lateral face of the motor housing;     -   a second radial compression stage including a second bladed         compression impeller coupled in rotation to the second section         of the motor shaft and having a second upstream end and a second         downstream end facing the side of the second lateral face of the         motor housing, such that the first bladed compression impeller         and the second bladed compression impeller are arranged in a         back-to-back configuration;     -   an outlet manifold secured to the motor housing and in         communication with the second downstream end of the second         bladed compression impeller;     -   a first cowl covering the first radial compression stage;     -   a second cowl covering the second radial compression stage; and     -   at least one inter-stage flow passage of gaseous fluid putting         the first downstream end of the first bladed compression         impeller into communication with the second upstream end of the         second bladed compression impeller;     -   wherein this inter-stage flow passage of gaseous fluid has the         following successive channels:     -   a main channel passing through the motor housing and provided         with a main inlet orifice opening onto the first lateral face of         the motor housing and in communication with the first downstream         end of the first bladed compression impeller;     -   an intermediate channel in sealed communication with the main         channel and passing through a spacer inserted between the second         lateral face of the motor housing and the second cowl; and     -   a secondary channel formed in the second cowl, and which is in         sealed communication with the intermediate channel, wherein said         secondary channel has a secondary outlet orifice opening out         facing the second upstream end of the second bladed compression         impeller.

Thus, the present disclosure proposes to put the gaseous fluid compressed at the outlet of the first stage in communication with the inlet of the second stage, passing through the motor housing, thus avoiding the use of an outer pipe. To do this, the inter-stage flow passage of gaseous fluid, or each of the inter-stage flow passages of gaseous fluid, comprises:

-   -   the main channel which recovers the gaseous fluid at the outlet         of the first bladed compression impeller (at the level of its         first downstream end), and which sends this gaseous fluid to the         other side of the motor housing (passing through it);     -   the intermediate channel, which extends the main channel in a         sealed manner, to pass through a spacer which makes it possible         to reach the second cowl while being isolated from the second         downstream end of the second bladed compression impeller; and     -   the secondary channel which extends the intermediate channel in         a sealed manner and which is provided in the second cowl to         redirect the gaseous fluid towards the center of the second         bladed compression impeller, at its second upstream end, so as         to enter the second compression stage.

In operation, the gaseous fluid (such as for example a gas or a gaseous mixture, such as air) is introduced into the first stage via the gaseous fluid inlet, and this gaseous fluid is sucked axially at the level of the first upstream end of the first bladed compression impeller, to be pressurized and then evacuated radially at its first downstream end. This gaseous fluid (which is compressed for the first time) then enters the main channel of the or each of the inter-stage flow passages of gaseous fluid, passes through the motor housing, and reaches the intermediate channel to pass through the spacer (without communication with the second downstream end of the second bladed compression impeller), then to access the secondary channel provided into the second cowl in order to be injected at the level of the second stage, and more precisely at the level of the second upstream end of the second bladed compression impeller, in order to be sucked axially at this second upstream end of the second bladed compression impeller, to be pressurized again and then to be evacuated radially at its second downstream end. The gaseous fluid is finally collected by the outlet manifold.

According to an embodiment, a first diffuser surrounds the first downstream end of the first bladed compression impeller and is provided with first fins distributed around said first downstream end of the first bladed compression impeller, wherein the first blades are separated by first exhaust flow paths, and wherein the main inlet of the main channel opens into one first exhaust flow path, between two first fins of the first diffuser.

Thus, the or each of the inter-stage flow passages of gaseous fluid takes the gaseous fluid from a first exhaust flow path of the first diffuser, at the outlet of the first stage, this first diffuser (also called stationary blading) filling a straightening function, by slowing down the gaseous fluid at the outlet of the first bladed compression impeller (at its first downstream end).

In a first embodiment, the first fins of the first diffuser are secured to the first lateral face of the motor housing, and the first cowl bears against these first fins.

In a second embodiment, the first fins of the first diffuser are secured to the first cowl, and the first fins bear against the first lateral face of the motor housing.

In a third embodiment, the first fins of the first diffuser are independent of the first cowl and of the motor housing, by being interposed between the first cowl and the first lateral face of the motor housing.

In particular, the spacer (or each of the spacers) is:

-   -   secured to the second lateral face of the motor housing, and the         second cowl bears against the spacer; or is     -   secured to the second cowl, and the spacer bears against the         second lateral face of the motor housing; or is     -   independent of the motor housing and the second cowl, by being         interposed between the second lateral face of the motor housing         and the second cowl.

In a particular embodiment, a second diffuser surrounds the second downstream end of the second bladed compression impeller and is provided with second fins distributed around said second downstream end of the second bladed compression impeller and interposed between the second lateral face of the motor housing and the second cowl, wherein the second fins are separated by second exhaust flow paths, and wherein the intermediate channel is provided through one of the second fins which thus forms the spacer.

Thus, at the outlet of the main channel of the or each of the inter-stage flow passages of gaseous fluid, the gaseous fluid passes through a second fin (forming a spacer) of the second diffuser, which makes it possible to pass through the second diffuser while being isolated from the second flow paths of this second diffuser.

In a first embodiment, the second fins of the second diffuser are secured to the second lateral face of the motor housing, and the second cowl bears against the second fins.

In a second embodiment, the second fins of the second diffuser are secured to the second cowl, and the second fins bear against the second lateral face of the motor housing.

In a third embodiment, the second fins of the second diffuser are independent of the motor housing and of the second cowl, by being interposed between the second lateral face of the motor housing and the second cowl.

According to one possibility, the motor housing is in one piece and the main channel passes through the motor housing.

Alternatively, the motor housing comprises an inner sleeve and an outer sleeve fitted into one another, and the main channel passes through the motor housing in an interface zone between the inner sleeve and the outer sleeve.

In this alternative, the main channel is provided on an outer peripheral face of the inner sleeve and/or on an inner peripheral face of the outer sleeve. This alternative is advantageous for manufacturing cost and simplicity reasons.

According to another possibility, the second cowl is in one piece and the secondary channel is provided in the second cowl.

Alternatively, the second cowl comprises an inner part and an outer part assembled on one another, and the secondary channel is provided in the second cowl in an interface zone between the inner part and the outer part.

In this alternative, the secondary channel is provided on an outer face of the inner part and/or on an inner face of the outer part. This alternative is advantageous for manufacturing cost and simplicity reasons.

According to one feature, the multi-stage centrifugal compressor further comprises a cooling circuit provided in the motor housing for a circulation of coolant inside the motor housing.

In this way, the gaseous fluid circulating in the main channel of the or each of the inter-stage flow passages of gaseous fluid, which is heated at the outlet of the first stage, can be cooled by heat exchange with this cooling circuit. Indeed, thanks to the present disclosure, this or these main channels are provided in the motor housing, in heat-conducting material, and therefore the surfaces offered by the main channel or channels and the circulation of water in the cooling circuit allow to evacuate the heat. In other words, the present disclosure makes it possible to use this cooling circuit for a dual purpose, namely to cool the rotary electric motor and cools the gaseous fluid passing from the first compression stage towards the second compression stage, which is interesting from a compact and also economical point of view.

According to one possibility, the cooling circuit has one or more sections contiguous to the main channel of the inter-stage flow passage of gaseous fluid or of one of the inter-stage flow passages of gaseous fluid.

In a particular embodiment, several inter-stage flow passages of gaseous fluid are provided.

According to one possibility, the main channels of the various inter-stage flow passages of gaseous fluid open into distinct first exhaust flow paths.

According to another possibility, the first diffuser comprises N first fins separated by N first exhaust flow paths wherein N is an integer greater than 2, and there are provided N inter-stage flow passages of gaseous fluid with N main channels which open in the respective first N exhaust flow paths.

According to one feature, the intermediate channels of the various inter-stage flow passages of gaseous fluid pass through distinct spacers.

According to another feature, the intermediate channels of the various inter-stage flow passages of gaseous fluid pass through distinct second fins (which, as a reminder, form spacers).

Advantageously, the second diffuser comprises N second fins wherein N is an integer greater than 2, and N inter-stage flow passages of gaseous fluid are provided with N intermediate channels which pass through the respective N second fins.

According to one feature, the main channel of the inter-stage flow passage of gaseous fluid or of one of the inter-stage flow passages of gaseous fluid extends in an axial direction parallel to the motor axis or substantially parallel to the motor axis; being understood by «substantially parallel» a maximum inclination between this axial direction and the motor axis of 10 degrees.

According to another feature, the main channel of the inter-stage flow passage of gaseous fluid or of one of the inter-stage flow passages of gaseous fluid has a variable cross-section along the motor axis.

Such a variation of the cross-section is advantageous for going from a main inlet orifice of suitable shape and dimensions to emerge on the first lateral face of the motor housing (and in particular in a first exhaust flow path), until reaching the intermediate channel which passes through the corresponding spacer (which can be a second fin) and which can therefore be of suitable shape and dimensions to pass through such a spacer (or second fin).

In a particular embodiment, the secondary channel of the inter-stage flow passage of gaseous fluid or of one of the inter-stage flow passages of gaseous fluid has a curved section between the corresponding intermediate channel and its secondary outlet orifice.

Such a curved section is advantageous for bringing the gaseous fluid leaving the concerned intermediate channel (in a direction more or less parallel to the motor axis), towards the center and in an opposite direction facing the second upstream end of the second bladed compression impeller.

According to one possibility, the curved section of the secondary channel has an angular amplitude comprised between 150 and 180 degrees, to define a reversal of the flow in said secondary channel.

According to another possibility, the second cowl is closed, without an orifice for introducing gaseous fluid opening into an outer face to introduce a gaseous fluid from the outside into the second stage of radial compression.

In other words, insofar as the gaseous fluid passes from the first stage to the second stage through the motor housing, then inside the second cowl, then this second cowl does not have to comprise an orifice shaped to introduce from the outside a gaseous fluid in the second stage of radial compression. However, it remains possible to provide at least one orifice passing through the second cowl for another function, for example for a sealed passage for a cable or a sensor.

According to one variant, the second cowl is fixed to the motor housing or to the outlet manifold.

According to one variant, the outlet manifold has an outlet volute in communication with the second downstream end of the second bladed compression impeller (and wherein applicable with the second exhaust flow paths of the second diffuser).

In an advantageous embodiment, the second diffuser comprises an annular body having two opposite annular planar faces, one of which forms the front face of the second diffuser and the other forms a face from which the second fins protrude.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present disclosure will appear on reading the detailed description below, of a non-limiting implementation, made with reference to the appended figures wherein:

FIG. 1 is a schematic side view of a multi-stage centrifugal compressor according to the present disclosure;

FIG. 2 is a schematic rear perspective view of part of the multi-stage centrifugal compressor of FIG. 1 , without the outlet manifold, the second bladed compression impeller and the second cowl;

FIG. 3 is a schematic perspective and exploded front view of the multi-stage centrifugal compressor of FIG. 1 ;

FIG. 4 is a schematic view in axial section of the multi-stage centrifugal compressor of FIG. 1 .

DETAILED DESCRIPTION

With reference to the figures, a multi-stage centrifugal compressor 1 according to an embodiment of the present disclosure comprises a rotary electric motor 2 arranged inside a motor housing 3, wherein the rotary electric motor 2 comprises a stator 20 arranged inside a housing of the motor housing 3, and a rotor 21 rotatably mounted in the stator 20 around a motor axis AM. The motor housing 3 has sealed orifices 30 for the passage of electrical power supply and control cables to the rotary electric motor 2.

The motor housing 3 has two opposite lateral faces, namely a first lateral face 31 and a second lateral face 32 which are transverse to the motor axis AM, as well as a peripheral face 33 extending around the rotary electric motor 2 and of the motor axis AM. The sealed orifices 30 are provided in the peripheral face 33. Feet 34 are also provided on the peripheral face 33 in order to be able to anchor the motor housing 3 and thus the multi-stage centrifugal compressor 1 to a frame, for example by screwing, bolting, welding or other equivalent fastening means.

The multi-stage centrifugal compressor 1 also comprises a motor shaft 4 driven in rotation around the motor axis AM by the rotary electric motor 2. This motor shaft 4 has two axial end sections, namely a first section 41 and a second opposite section 42 extending on either side of the rotary electric motor 2 and the motor housing 3. The first section 41 extends beyond the first lateral face 31 of the motor housing 3, and the second section 42 extends beyond the second lateral face 32 of the motor housing 3.

Moreover, a cooling circuit 36 is provided in the motor housing 3 for a circulation of coolant inside the motor housing 3, about the rotary electric motor 2, with an inlet 37 and an outlet 38 leading to the peripheral face 33 for fluid communication of the cooling circuit 36 with a source of coolant (not shown).

The multi-stage centrifugal compressor 1 comprises a first radial compression stage 5 and a second radial compression stage 6 configured to successively compress a gaseous fluid, and arranged on either side of the rotary electric motor 2 and of the motor housing 3.

The first radial compression stage 5 comprises a first bladed compression impeller 50 (also called wheel or bladed impeller) coupled in rotation to the first section 41 of the motor shaft 4 to be driven in rotation around the motor axis AM. This first bladed compression impeller 50 has:

-   -   a first upstream end 51 in communication with a gaseous fluid         inlet 80; and     -   a first downstream end 52 surrounded by a first diffuser 53.

The first downstream end 52 is turned towards the side of the first lateral face 31 of the motor housing 3 so that, along the motor axis AM, the first upstream end 51 is more distant from the motor housing 3 compared to the first downstream end 52.

The multi-stage centrifugal compressor 1 comprises a first cowl 8 covering the first radial compression stage 5 and fixed to the first lateral face 31 of the motor housing 3. This first cowl 8 has in its center an inlet opening forming a gaseous fluid inlet 80, placed facing the first upstream end 51 of the first bladed compression impeller 50. This gaseous fluid inlet 80 is centered on the motor axis AM.

The first bladed compression impeller 50 has an increasing diameter from the first upstream end 51 to the first downstream end 52, and it has blades (also called vanes) which define between them compression channels which are, on the one hand, open at the first upstream end 51 for an inlet of the gaseous fluid and, on the other hand, open at the first downstream end 52 for an outlet of the compressed gaseous fluid.

The function of the first diffuser 53 is to straighten and slow down the compressed gaseous fluid at the outlet of the first bladed compression impeller 50. To do this, the first diffuser 53 is provided with first fins 54 distributed around the first downstream end 52 of the first bladed compression impeller 50 and separated by first exhaust flow paths 55. These first exhaust flow paths 55 thus form spaces between the first fins 54, and they are in communication with and in the extension of the compression channels of the first bladed compression impeller 50.

Moreover, the first diffuser 53 is secured to the first lateral face 31 of the motor housing 3. Thus, the first fins 54 are secured to the first lateral face 31 of the motor housing 3, for example by being formed in one piece with this first lateral face 31. The first fins 54 protrude from the first lateral face 31, and can for example be of triangular or polygonal shape in general.

In a non-illustrated variant, the first diffuser 53 is secured to the first cowl 8 and is pressed against the first lateral face 31 of the motor housing 3. In other words, in this variant, the first fins 54 are secured and protrude from the first cowl 8, for example by being formed in one piece with this first cowl 8, and they are pressed against the first lateral face 31 of the motor housing 3.

The second radial compression stage 6 comprises a second bladed compression impeller 60 (also called wheel or bladed impeller) coupled in rotation to the second section 42 of the motor shaft 4 to be driven in rotation around the motor axis AM. This second bladed compression impeller 60 has:

-   -   a second upstream end 61; and     -   a second downstream end 62 surrounded by a second diffuser 63         secured to the second lateral face 32 of the motor housing 3.

The second downstream end 62 is turned towards the side of the second lateral face 32 of the motor housing 3 so that, along the motor axis AM, the second upstream end 61 is more distant from the motor housing 3 compared to the second downstream end 62. Thus, the first bladed compression impeller 50 and the second bladed compression impeller 60 are arranged in a back-to-back configuration. Such a back-to-back assembly is advantageous for subtracting the forces of the two bladed compression impellers 50, 60 on the motor shaft 4, the resulting force then being less and easier to compensate for increasing the life of the multi-stage centrifugal compressor 1.

The second bladed compression impeller 60 has an increasing diameter from the second upstream end 61 to the second downstream end 62, and it has blades (also called vanes) which define between them compression channels which are, on the one hand, open at the second upstream end 61 for an inlet of the gaseous fluid and, on the other hand, open at the second downstream end 62 for an outlet of the compressed gaseous fluid.

The function of the second diffuser 63 is to straighten and slow down the compressed gaseous fluid at the outlet of the second bladed compression impeller 60. To do this, the second diffuser 63 is provided with second fins 64 distributed around the second downstream end 62 of the second bladed compression impeller 60 and separated by second exhaust flow paths 65. These second exhaust flow paths 65 thus form spaces between the second fins 64, and they are in communication with and in the extension of the compression channels of the second bladed compression impeller 60.

The second fins 64 are secured to the second lateral face 32 of the motor housing 3, for example by being formed in one piece with this second lateral face 32. The second fins 64 protrude from the second lateral face 32, and can for example be triangular or polygonal in general.

The second diffuser 64 also has an annular body 66 (or annular ring) having two opposed flat annular faces 67, 68, one of which 67 forms a front face and the other 68 forms a dorsal face from which the second fins protrude 64. Thus, these second fins 64 extend between the second lateral face 32 and the dorsal face 68 of the annular body 66, and the second downstream end 62 of the second bladed compression impeller 60 is housed inside the second diffuser 64 to be surrounded by the second fins 64.

The multi-stage centrifugal compressor 1 comprises a second cowl 9 covering the second radial compression stage 6 and secured to the outlet manifold 7. This second cowl 9 comprises an inner face (turned towards the motor housing 3 and the second stage of radial compression 6) on which is provided an annular bearing face 90 which bears against the front face 67 of the second diffuser 64. This second cowl 9 comprises an outer face 91, opposite to the inner face, and which is turned on the outside.

In a non-illustrated variant, the second diffuser 64 is secured to the second cowl 9, so that the second fins 64 are secured to and protrude from the second cowl 9, for example by being formed in one piece with this second cowl 9, and they are pressed against the second lateral face 32 of the motor housing 3.

The multi-stage centrifugal compressor 1 comprises an outlet manifold 7 secured to the motor housing 3, which has an outlet volute 70 in communication with the second exhaust flow paths 65 of the second diffuser 63. This outlet manifold 7 is fixed on a annular flange 35 provided on the peripheral face 33 of the motor housing 3, so that the outlet volute 70 surrounds the second diffuser 63 and its second exhaust flow paths 65.

The multi-stage centrifugal compressor 1 comprises several inter-stage flow passages of gaseous fluid 10 communicating:

-   -   the first downstream end 52 of the first bladed compression         impeller 50, and in particular the first exhaust flow paths 55         of the first diffuser 53 of the first radial compression stage         5;

with

-   -   the second upstream end 61 of the second bladed compression         impeller 60.

Each inter-stage flow passage of gaseous fluid 10 comprises at least:

-   -   a main channel 11 made through the motor housing 3 and provided         with a main inlet 111 opening into a first exhaust flow path 55,         between two first fins 54 of the first diffuser 53, so as to         open into the first lateral face 31 of the motor housing 3 to be         in communication with the first downstream end 52 of the first         bladed compression impeller 50;     -   an intermediate channel 12 in sealed communication with the main         channel 11 and passing through a second fin 64 of the second         diffuser 63 to emerge on the front face 67 of the second         diffuser 63, this second fin 64 thus forming a spacer inserted         between the second lateral face 32 of the motor housing 3 and         the second cowl 9, wherein this intermediate channel 12 is         provided with a main outlet orifice 112 opening into the front         face 67;     -   a secondary channel 13 formed in the second cowl 9 which is         pressed against the front face 67 of the second diffuser 63,         this secondary channel 13 comprising a secondary inlet orifice         131 opening into the annular bearing face 90 of the second cowl         9 and in communication with the main outlet orifice 112 of the         intermediate channel 12, and a secondary outlet orifice 132         opening into the inner face of the second cowl 9 opposite the         second upstream end 61 of the second bladed compression impeller         60 to form all or part of a gaseous fluid inlet within the         second compression stage 6.

Thus, the gaseous fluid is introduced into the multi-stage centrifugal compressor 1 via the gaseous fluid inlet 80 formed in the first cowl 8, then it is compressed in the first bladed compression impeller 50 to come out at its first downstream end 52, and then the compressed gaseous fluid is straightened in the first exhaust flow paths 55 of the first diffuser 53, and it enters inside the main channels 11, then it passes through the intermediate channels to pass through the second fins 64 of the second diffuser 63 (without being in communication with the second exhaust flow paths 65) to enter the secondary channels 13, which will allow the compressed gaseous fluid to come out opposite the second upstream end 61 of the second bladed compression impeller 60, and thus this compressed gaseous fluid is compressed in the second bladed compression impeller 60 to emerge at its second downstream end 62, and the compressed gaseous fluid thus compressed twice is collected in the outlet manifold 7.

In this way, between the first stage of radial compression 5 and the second stage of radial compression 6, the inter-stage flow passages of gaseous fluid 10 do not exit on the outside of the multi-stage centrifugal compressor 1, but are provided entirely inside the motor housing 3, the second fins 64 of the second diffuser 63 and the second cowl 9.

It should be noted that the secondary channels 13 do not open into the outer face 91 of the second cowl 9, but only open into its inner face at the level of their secondary inlet orifices 131 and their respective secondary outlet orifices 132.

It should also be noted that, in the particular embodiment wherein the second fins 64 are secured to the motor housing 3, then the main channel 11 and the intermediate channel 12 together form a single and same channel. On the other hand, in the variant wherein the second fins 64 are secured to the second cowl 9, then the secondary channel 13 and the intermediate channel 12 together form a single and same channel.

In addition, to arrange the main channels 11 through the motor housing 3, it is possible to have a motor housing 3 comprising two parts, namely:

-   -   an inner sleeve inside which the rotary electric motor 2 is         arranged, and     -   an outer sleeve fitted contiguously around the inner sleeve;

wherein the main channels 11 are arranged in a peripheral interface zone between the inner sleeve and the outer sleeve.

In other words, the main channels 11 are arranged on an outer peripheral face of the inner sleeve and/or on an inner peripheral face of the outer sleeve.

Similarly, to arrange the secondary channels 13 in the second cowl 9, it is possible to have a second cowl 9 comprising two parts, namely:

-   -   an inner part turned on the side of the second radial         compression stage 6, and     -   an outer part joined together on the inner part and facing the         outside;

wherein the secondary channels 13 are arranged in an interfacing zone between the inner part and the outer part.

In other words, the secondary channels 13 are provided on an outer face of the inner part and/or on an inner face of the outer part.

Moreover, the cooling circuit 36, provided in the motor housing 3, has one or more sections contiguous to the main channels 11, which has the advantage of cooling the compressed gaseous fluid leaving the first stage of radial compression 5, before entering the second radial compression stage 6. Such cooling of the gaseous fluid between the two radial compression stages 5, 6 makes it possible to increase the density of the gaseous fluid and thus to reduce the sections of the main channels 11. In addition, the cooling of the gaseous fluid between the two radial compression stages 5, 6 makes it possible to limit the final temperature of the gaseous fluid and therefore the energy consumption, and thus to improve the performance of the multi-stage centrifugal compressor 1.

It is conceivable that the first diffuser 53 comprises N first fins 54 separated by N first exhaust flow paths 55 wherein N is an integer greater than 2 (for example an integer greater than or equal to 10), the second diffuser 63 comprises N second fins 64, and N inter-stage flow passages of gaseous fluid 10 are provided with N main channels 11 which open into the N respective first exhaust flow paths 55 and N associated intermediate channels 12 which pass through the respective N second fins 64. Thus, N secondary channels 13 are provided in the second cowl 9, and moreover the main channels 11 open into first distinct exhaust flow paths 55 and the N intermediate channels 12 pass through second distinct fins 64.

Each main channel 11 extends in an axial direction parallel to the motor axis AM or substantially parallel to the motor axis AM, being understood by «substantially parallel» a maximum inclination between this axial direction and the motor axis AM of 10 degrees.

Furthermore, the shape and dimensions of the main inlet orifices 111 depend on the shape and dimensions of the first exhaust flow paths 55, and likewise the shape and dimensions of the main outlet orifices 112 depend on the shape and dimensions of the second fins 64. Also, insofar as the first exhaust flow paths 55 do not have the same shapes and dimensions as the second fins 64, then the main inlet orifices 111 do not have the same shapes and dimensions than the main outlet orifices 112. Therefore, each main channel 11 has a variable cross-section between its main inlet orifice 111 and the main outlet orifice 112.

Each secondary channel 13 has a curved section between its secondary inlet orifice 131 and its secondary outlet orifice 132, according to an angular amplitude comprised between 150 and 180 degrees, to define a reversal of the flow in the secondary channel 13. Indeed, as each secondary channel 13 only opens into the inner face of the second cowl 9 at its secondary inlet orifice 131 and its secondary outlet orifice 132, the secondary channel 13 causes the fluid to make a sort of U-turn compressed gas. The secondary outlet orifices 132 are provided at the level of the center of the second cowl 9. Deflector flaps 92 can be provided on the second cowl 9, opposite the secondary outlet orifices 132 of each secondary channel 13, in order to deflect the gaseous fluid leaving the secondary channels 13 in the direction of the second downstream end 62 of the second bladed compression impeller 60.

It should also be noted that the second cowl 9 is closed, without an orifice for introducing gaseous fluid opening into its outer face 91 to introduce a gaseous fluid from the outside into the second stage of radial compression. In other words, the only gaseous fluid entering the second stage of radial compression is that coming from the secondary channels 13. It is of course possible to provide an orifice passing through the second cowl 9, for example for a sealed passage of a cable or a sensor, but not for introducing a gaseous fluid from the outside into the second stage of radial compression. 

1. A multi-stage centrifugal compressor, comprising: a rotary electric motor arranged inside a motor housing having two opposite lateral faces, namely a first lateral face and a second lateral face; a motor shaft driven in rotation around a motor axis by the rotary electric motor and having a first section and a second section opposite each other extending on either side of the rotary electric motor and of the two respective lateral faces of the motor housing; a first radial compression stage comprising a first bladed compression impeller coupled in rotation to the first section of the motor shaft and having a first upstream end in communication with a gaseous fluid inlet, and a first downstream end facing the side of the first lateral face of the motor housing; a second radial compression stage comprising a second bladed compression impeller coupled in rotation to the second section of the motor shaft and having a second upstream end and a second downstream end facing the side of the second lateral face of the motor housing so that the first bladed compression impeller and the second bladed compression impeller are arranged in a back-to-back configuration; an outlet manifold secured to the motor housing and in communication with the second downstream end of the second bladed compression impeller; a first cowl covering the first radial compression stage; a second cowl covering the second radial compression stage; and at least one inter-stage flow passage of gaseous fluid communicating the first downstream end of the first bladed compression impeller with the second upstream end of the second bladed compression impeller; wherein the at least one inter-stage flow passage of gaseous fluid has the following successive channels: a main channel passing through the motor housing and provided with a main inlet orifice opening onto the first lateral face of the motor housing and in communication with the first downstream end of the first bladed compression impeller; an intermediate channel in sealed communication with the main channel and passing through a spacer inserted between the second lateral face of the motor housing and the second cowl; and a secondary channel formed in the second cowl and which is in sealed communication with the intermediate channel, wherein the secondary channel has a secondary outlet orifice opening opposite the second upstream end of the second bladed compression impeller.
 2. The multi-stage centrifugal compressor according to claim 1, wherein a first diffuser surrounds the first downstream end of the first bladed compression impeller and is provided with first fins distributed around the first downstream end of the first bladed compression impeller, wherein the first fins are separated by first exhaust flow paths, and wherein the main inlet orifice of the main channel opens into one first exhaust flow path, between two first fins of the first diffuser.
 3. The multi-stage centrifugal compressor according to claim 2, wherein the first fins of the first diffuser are: secured to the first lateral face of the motor housing, and the first cowl bears against the first fins; or are secured to the first cowl, and the first fins bear against the first lateral face of the motor housing; or are independent of the first cowl, and the motor housing, by being interposed between the first cowl and the first lateral face of the motor housing.
 4. The multi-stage centrifugal compressor according to claim 1, wherein the spacer is: secured to the second lateral face of the motor housing, and the second cowl bears against the spacer; or is secured to the second cowl, and the spacer bears against the second lateral face of the motor housing; or is independent of the motor housing and the second cowl, by being interposed between the second lateral face of the motor housing and the second cowl.
 5. The multi-stage centrifugal compressor according to claim 1, wherein a second diffuser surrounds the second downstream end of the second bladed compression impeller and is provided with second fins distributed around the second downstream end of the second bladed compression impeller and interposed between the second lateral face of the motor housing and the second cowl, wherein the second fins are separated by second exhaust flow paths, and wherein the intermediate channel is arranged through one of the second fins which thus forms the spacer.
 6. The multi-stage centrifugal compressor according to claim 5, wherein the second fins of the second diffuser are: secured to the second lateral face of the motor housing, and the second cowl bears against the second fins; or are secured to the second cowl, and the second fins bear against the second lateral face of the motor housing; or are independent of the motor housing and the second cowl, by being interposed between the second lateral face of the motor housing and the second cowl.
 7. The multi-stage centrifugal compressor according to claim 1, wherein: the motor housing is in one piece and the main channel passes through the motor housing, or the motor housing comprises an inner sleeve and an outer sleeve fitted into one another and the main channel passes through the motor housing in an interface zone between the inner sleeve and the outer sleeve.
 8. The multi-stage centrifugal compressor according to claim 1, wherein: the second cowl is in one piece and the secondary channel is provided in the second cowl, or the second cowl comprises an inner part and an outer part assembled on one another and the secondary channel is provided in the second cowl in an interface zone between the inner part and the outer part.
 9. The multi-stage centrifugal compressor according to claim 1, further comprising a cooling circuit arranged in the motor housing for a circulation of coolant inside the motor housing.
 10. The multistage centrifugal compressor according to claim 9, wherein the cooling circuit has one or more sections contiguous to the main channel of the at least one inter-stage flow passage of gaseous fluid or one of the at least one inter-stage flow passage of gaseous fluid.
 11. The multi-stage centrifugal compressor according to claim 1, wherein a plurality of inter-stage flow passages of gaseous fluid are provided.
 12. The multi-stage centrifugal compressor according to claim 2, wherein the main channel of the at least one inter-stage flow passage of gaseous fluid opens into distinct first exhaust flow paths.
 13. The multi-stage centrifugal compressor according to claim 12, wherein the first diffuser comprises N first fins separated by N first exhaust flow paths wherein N is an integer greater than 2, and N inter-stage flow passages of gaseous fluid are provided with N main channels which open into the N respective first exhaust flow paths.
 14. The multi-stage centrifugal compressor according to claim 11, wherein the intermediate channel of the at least one various inter-stage flow passage of gaseous fluid passes through distinct spacers.
 15. The multi-stage centrifugal compressor according to claim 5, wherein the at least one inter-stage flow passage of gaseous fluid is a plurality of inter-stage flow passages of gaseous fluid and intermediate channels of the different inter-stage flow passages of gaseous fluid of the plurality of inter-stage flow passages of gaseous fluid pass through distinct second fins.
 16. A multi-stage centrifugal compressor according to claim 15, wherein the second diffuser comprises N second fins wherein N is an integer greater than 2, and there are N inter-stage flow passages of gaseous fluid with N intermediate channels passing through the respective N second fins.
 17. The multistage centrifugal compressor according to claim 1, wherein the main channel of the at least one inter-stage flow passage of gaseous fluid or of one of the at least inter-stage flow passage of gaseous fluid extends along an axial direction parallel to the motor axis or substantially parallel to the motor axis.
 18. The multi-stage centrifugal compressor according to claim 1, wherein the main channel of the at least one inter-stage flow passage of gaseous fluid or of one of the at least one inter-stage flow passage of gaseous fluid has a variable cross-section along the motor axis (AM).
 19. The multistage centrifugal compressor according to claim 1, wherein the secondary channel of the at least one inter-stage flow passage of gaseous fluid or of one of the at least one inter-stage flow passage of gaseous fluid has a curved section between a corresponding intermediate channel and its secondary outlet.
 20. The multi-stage centrifugal compressor according to claim 19, wherein the curved section of the secondary channel has an angular amplitude comprised between 150 and 180 degrees, to define a reversal of flow in the secondary channel.
 21. The multi-stage centrifugal compressor according to claim 1, wherein the second cowl is closed, without a gaseous fluid introduction orifice opening into an outer face to introduce from outside a gaseous fluid in the second of radial compression stage.
 22. The multi-stage centrifugal compressor according to claim 1, wherein the second cowl is fixed to the motor housing or to the outlet manifold.
 23. The multi-stage centrifugal compressor according to claim 1, wherein the outlet manifold has an outlet volute in communication with the second downstream end of the second bladed compression impeller. 